Saving Seafood

Low oxygen is pushing fish into shallower water

September 21, 2021 — Fish can drown. They require oxygen to breathe, and use the oxygen dissolved in water rather than that in the air. When there’s too little oxygen in the water, they have to move or suffer ill effects.

Unfortunately, oxygen concentrations are dropping throughout the oceans. The new research, published in Global Change Biology, spans 15 years of surveys and measurements. The authors stress the importance of accounting for the findings in fishery management and conservation, or risk implementing strategies wildly out of step with conditions under the waves.

“This study finds that oxygen is declining at all the depths we surveyed: from 50 meters (164 feet) to 350 meters (1,148 feet),” says lead author Erin Meyer-Gutbrod, “and so fish seem to be moving up to shallower regions to get to an area where the oxygen is relatively higher.” Now an assistant professor at the University of South Carolina, Meyer-Gutbrod started this analysis as a postdoctoral scholar at the University of California, Santa Barbara.

Oxygen concentrations are decreasing for a number of reasons, including changes in ecology, seasons, and storms. But perhaps the most significant reason is that warmer water holds less dissolved oxygen.

Read the full story at Futurity

 

From tiny phytoplankton to massive tuna: How climate change will affect energy flows in ocean ecosystems

January 24, 2017 — Phytoplankton are the foundation of ocean life, providing the energy that supports nearly all marine species. Levels of phytoplankton in an ocean area may seem like a good predictor for the amount of fish that can be caught there, but a new study by Nereus Program researchers finds that this relationship is not so straightforward.

“Using measurements of phytoplankton growth at the base of the food web to estimate the potential fish catch for different parts of the ocean has long been a dream of oceanographers,” says author Ryan Rykaczewski, Assistant Professor at University of South Carolina and Nereus Program Alumnus. “We know that these two quantities must be related, but there are several steps in the food chain that complicate the conversion of phytoplankton growth to fish growth.”

Published today in PNAS, the study uses a mathematical model to explore the processes that mediate the transfer of energy from the base of the food web to fish. The authors found that there are large regional differences in fish catch because of how surface ocean and bottom ecosystems channel energy sources.

“Coastal systems where large amounts of nutrients critical for phytoplankton growth are ‘upwelled’ from deep waters via currents make a contribution to global fish catch that far exceeds what one would expect from phytoplankton production alone,” says lead author Charles Stock, Research Oceanographer at NOAA/Geophysical Fluid Dynamics Laboratory and Nereus Program Principal Investigator.

Read the full story at Phys.org